I use one as a trainer for myself, and for the students i teach at our county range. It has done very well for me, though it gets very dirty in short order.
Performance has been stellar, with the exception of winchester .22lr of any variety... everything else has been basically 100% effective. Accuracy is reasonable for the design, i'm overall very pleased with it.
A word of caution though... I would encourage you NOT to detail strip the frame for cleaning but rather blast it with BWC gunscrubber or something similar that is polymer safe. It's a PITA to get it all back in correctly, and it is very easy to crack the hammer spring housing. S&W offered to replace mine (lifetime coverage they said) but would not give/sell me the plastic part of the frame (which is not serialized) even though I am a certified armorer. The guy told me they might replace the entire gun, which is asinine over something so easy to change. I do not desire a serial number change and additional paperwork to get my own damn gun back, so i said no. It is functional as is, even with the crack- I'm going to fill the rear frame cavity behind that housing with devcon and call it a wash. They did offer to pay shipping, which was nice.
My last remaining gripe is with all M&P series handguns, though they are still my favorite of the poly frame guns: ROLL PINS! WTF?!?!!? if glock can use a standard pin in all their models, the m&p ought to do the same. Roll pins are a cheap out on the part of the MFG, and IMHO a weak link in this handgun. After a few detail strips, it's very easy to bugger them up and/or bend them. If I keep my m&p guns, which I likely will, I intend to cut some cylinder pins for them.
Overall, i'm happy with the pistol but less than impressed with S&W service. The guy on the phone was very nice (after 30+ min on hold), but the solutions are less than satisfactory.